Cable television systems provide a method of television signal distribution between a central facility generally referred to as the "headend", and a large number of television viewers through a cable distribution system. The headend includes the source of programming information together with a plurality of television channel modulators which provide a plurality of television program signals at different channel frequencies. The plurality of program channel signals are communicated to the individual television viewers via a network of cables, distribution equipment, and individual signal decoders at each user location. Early cable television systems were usually limited to one-way cable systems so named because all communication occurred from the headend down through the system to the individual decoders. Later developed systems provided communication capability in both directions between the headend and encoders and are thus referred to as two-way cable television systems. For purposes of convenience, communications and information transmission from the headend to the user decoders is generally referred to as "downstream" communication while the transmission of information and data from the user decoders to the headend of the system is referred to as "upstream" communication.
Downstream signals or communication typically include program information together with appropriate television scan synchronizing information plus additional data such as subscriber addresses or program authorization. This additional data is usually combined with the program information during the vertical blanking interval of the signal. Typical upstream signals or information may include program purchases or other relevant information such as responses to status inquiry or polling information requests.
In most cable television systems, the various program channels are grouped into basic service channels together with special optional channels which require additional service fees or payments to be received by the viewer. The latter are generally referred to as pay channels or programs and may be received and displayed solely by those decoders within the cable system which are authorized to view them. In virtually all cable television systems, the need for authorization to receive and display pay programming is enforced by the use of scrambled signals on pay channels. At the headend of the system, a signal scrambler is operative upon the program information to alter it in a manner rendering it virtually unviewable when applied unchanged to a television receiver. At the encoder, a corresponding descrambler is operative to unscramble the program information and return it to the proper television format for viewing on a conventional television receiver. The headend further includes an address computer and signal encoder which cooperate to insert the program authorization information for the pay per view channel within the vertical blanking interval. Correspondingly, the encoder includes systems for responding to the authorization information within the vertical blanking interval to activate the descrambler once the proper authorization signal is received.
When a cable television viewer attempts to receive a particular program channel, the encoder is tuned to the selected channel and the encoder determines whether the appropriate authorization code is present during the program signal vertical blanking interval. The presence of the appropriate authorization code indicates that the decoder is authorized to receive the pay program information and the descrambler is activated and the program information is properly displayed. If, however, the correct authorization code is not carried within the program signal, the decoder is not authorized to receive the pay per view program and the signal will not be descrambled. In some cable television systems, unauthorized pay programs are simply displayed in their scrambled form and are thus unviewable. In other systems, however, a viewer request for an unauthorized pay signal causes the decoder to be switched to an alternate channel which provides additional information to the viewer. Such alternate channels are generally referred to as "barker" channels and the process of automatically switching to such alternate channels is generally referred to as "barkering". In their simplest form, barker channels may simply display information to the viewer indicating that the viewer is not authorized to receive the selected program and may suggest that the viewer subscribe to the pay channel. More likely, however, the viewer is afforded the opportunity to obtain authorization immediately in a process often referred to as individual or impulse pay per view.
The information within the information packet inserted into the vertical blanking interval of the program signal in most cable television systems includes a decoder address or unique identifier for the particular decoder for which the communication is intended. In addition, some cable television systems provide a market code identifier which specifies a particular group of decoders from within the larger number of decoders in the system. The initial purpose for the use of such market code identifiers was to prevent the use of a viewer's decoder in another geographic or market area rather than the geographic or market area in which the cable system operator originally installed the decoder. In part, this provides some measure of theft prevention since the reuse of decoders in other areas is thwarted. It has also been found, however, that the use of market codes in addition to the decoder address system enables the cable operator to divide the cable system into a plurality of subgroups or units which may be handled individually or differently thereby increasing system flexibility. With these benefits available, the use of market coded cable systems has increased and, most likely, will continue.
While many present cable systems have been successful in providing a great number of program channels to the viewer, and have provided tiered systems using market codes, there remains a continuing need in the art for evermore flexible and improved cable television systems.
Accordingly, it is a general object of the present invention to provide an improved cable television system. It is a more particular object of the present invention to provide an improved cable television system which exhibits additional system flexibility and a multiple tiered capability.